MAXILLARY AND VOMER BONES OF POLYPTERUS 361 
Internal (posteromesial) to the maxillary and premaxillary 
teeth, between them and the external edges of the ectopterygoids 
and so-called vomers, there is a well-developed sulcus, and 
internal (posteromesial) to the vomers there is a depressed region 
bounded on either side by a suleus which passes slightly be- 
neath (dorsal to) the vomer and ends, posteriorly, along the 
mesial edge of the anterior end of the ectopterygoid. This latter 
sulcus thus certainly corresponds to the postpalatine furrow of 
Acanthias, and the vomers certainly lie, in part, in a palatine 
fold. The only question then is, does the furrow that, in Po- 
lypterus, lies between the vomer and the premaxillary teeth 
correspond to the furrow that, in Acanthias, les between the 
palatine fold and the palatine teeth, or to the sulcus that lies ex- 
ternal to the latter teeth; and there seems no question that it 
corresponds to the latter sulcus, and hence is a primary superior 
alveololabial sulcus, for its posterior continuation lies definitely 
along the lateral edge of the ectopterygoid. 
The premaxillomaxillary dental arcade of Polypterus is thus a 
secondary one, but it apparently lies directly along the line of 
the primary lip, instead of anterior to that lip. A slight sulcus, 
only, separates the premaxillary teeth from the ventral edge of 
the secondary lip, this suleus becoming, opposite the maxillary 
teeth, the well-developed secondary alveololabial sulcus already 
described. Posterior to the most posterior maxillary tooth, this 
secondary alveololabial sulcus and the primary one are sepa- 
rated, for a certain distance, by a ridge of the mucous lining 
membrane of the roof of the mouth, but this ridge gradually 
diminishes posteriorly, and vanishes at the anterior edge of the 
lateralprocess of the ectopterygoid. The primary and secondary 
alveololabial sulci are then represented, for a certain distance, by 
a single sulcus, which passes ventral to the lateral process of the 
ectopterygoid and vanishes posterior to the angle of the gape. 
The fold of the secondary upper lip has thus been carried 
forward until it falls into its fellow of the opposite side at the 
anterior end of the snout, but in its anterior portion it passes so 
close to the primary lip that it is there but slightly differentiated 
from it. In accord with this, and also in confirmation of it, 
